High intensity light, including laser light, can permanently damage vision. The potentially injurious light may be emitted by military weapons or by industrial equipment. In some instances the wavelength of the potentially injurious light is known. In these instances, eyewear has been employed to filter a narrow band or "notch" of spectral wavelengths corresponding to the objectionable light. Notch filters may be acceptable in some industrial workplaces where the objectionable light can be fairly accurately predicted. However, eye damage may occur in situations where the filtering abilities of the prior art notch filter eyewear do not closely match the wavelength of the objectionable light.
Other prior art protective "broadband" filter eyewear has reduced the amount of all wavelengths of light passing therethrough. However, these broadband filters result in poor seeing, including reduced visual acuity and poor color differentiation.
Laser weapons capable of causing severe and permanent eye damage have been developed in recent years. The wavelengths of some such weapons have been publicly reported. However, laser weapons emitting light of other wavelengths are possible and may be under development. The inability to accurately predict the wavelength of laser light that may be developed and/or employed under combat conditions makes it difficult to develop an acceptable notch filter for blocking that particular wavelength of light. Prior art broadband filters are unacceptable for most combat situations because of the poor seeing associated with such filters.
It has generally and intuitively been assumed that the quality of vision varies directly with the amount of light available to the viewer. However, these assumptions are not correct. In fact some wavelengths of ambient light actually degrade the quality of vision. William A. Thornton has taught that illumination for good seeing by human beings requires only three "prime" colors which define narrow spectral bands centered approximately at 450 nanometers, 530 nanometers, and 610 nanometers. Thornton has developed illumination to generate light mainly at these three narrow prime color spectral wavelength bands. Although the light produced by the Thornton illumination is "dim", images seen in this "dim" light actually appear quite bright and yield accurate color differentiation. Thus, the Thornton illumination teaching enables efficient light to be produced with substantially reduced power.
Thornton's teaching is further presented in U.S. Pat. No. 3,877,797 which proposes a pair of goggles made from didymium glass lenses to remove 580 nanometer light and a porphyrin chelate film to remove 490 nanometer light, while passing the remainder of the visible spectrum. Scenes viewed through these goggles appear approximately as bright as the same scene viewed without the goggles. In particular, daylight viewed through the goggles appeared "white" and color discrimination through the goggles was equivalent to color discrimination without the goggles.
The goggles shown in U.S. Pat. No. 3,877,797 are of some intellectual interest, but would be of limited usefulness in an industrial work place, and would be of virtually no use in the above described military applications intended to protect against laser weapons. In particular, the goggles shown in U.S. Pat. No. 3,877,797 do not block a sufficient amount of light to prevent eye damage to a viewer in many combat situations or industrial work places. Consequently, the goggles shown in U.S. Pat. No. 3,877,797 have little practical application.
In view of the above, it is an object of the subject invention to provide protective eyewear that blocks substantial portions of approaching light, while simultaneously enabling good seeing.
Another object of the subject invention is to provide filters which permit only selected narrow spectral wavelength bands of light to pass therethrough while still enabling good seeing.
It is an additional object of the subject invention to provide a broadband filter that permits three narrow spectral wavelength bands to pass therethrough.
A further object of the subject invention is to provide filtering lenses which block over 90% of the visible spectrum of light but enable good seeing.